A technology superseded by Flatpaks, yet pushed incessantly by Canonical, a befuddling move that I still don't quite understand. Rough to use in any other distro.
> AppImages
Speaking from experience, these don't run on every distro. So they fail to fulfill their intended purpose. As far as I'm concerned, that makes distributing software as AppImages a no-go.
> Flatpak
Better than any of the technologies previously quoted, but it is not without it's own issues. The chances of a Flatpak working on any particular distro are acceptably high, but they still suffer from the same problem AppImages do. I've had an instance were a an app refused to run on OpenSUSE, even though it was working completely fine on Fedora (I was using Flathub's repo on both distros, I wasn't using Fedora's, just to clarify). I think it was Firefox, though I'm not 100% on that.
Still, I'm yet to see a commercial software being distributed as a Flatpak. My guess is that it's all more of a hassle than it is worth. Which, I guess you could say that about packaging commercial software for Linux in general. So, we're back to square one with the chicken and the egg problem that Linux suffers from. Though nowadays it's less severe what with the existence of SteamOS and all of that, so at least there is a substantial marketshare, small as it is.
EDIT: fixed vertical spacing.
Most commercial software in general can be downloaded as a free demo version and then activated with a license key or account, and that model works really well with Flatpak and even Flathub.